Heavy metals such as mercury can be present in trace amounts in hydrocarbon gases, crude oils, and produced water. The amount can range from below the analytical detection limit to several thousand ppbw (parts per billion by weight) depending on the source. Crudes containing 50 ppbw total mercury or more are referred to herein as high mercury crudes. When processed in the distillation furnace in a refinery, the particulate mercury in high mercury crudes decomposes to elemental mercury which accumulates in the distillation column overhead, and possibly contaminates the light liquid products and the gas products. In addition, liquid elemental mercury may accumulate in some equipment. If mercury is removed from crude oil, a mercury-containing waste product is generated. In order to minimize the volume and cost of disposal of this waste, it is desired that the waste have as high a mercury content as possible. In addition the mercury in the waste should be essentially non-leachable and pass TCLP (toxicity characteristic leaching procedure) requirements.
There are processes in the prior art to remove mercury in crude oils, but these generate either a gaseous mercury-containing waste product, an aqueous mercury-containing waste product, or a dilute solid waste product that contains less than about 100 ppm Hg and is therefore produced in large volumes. Various methods to remove trace metal contaminants in liquid hydrocarbon feed such as mercury have been disclosed, including the removal of mercury from water by iodide impregnated granular activated carbons. U.S. Pat. No. 5,336,835 discloses the removal of mercury from liquid hydrocarbon using an adsorbent comprising an activated carbon impregnated with a reactant metal halide, with the halide being selected from the group consisting of I, Br and Cl. U.S. Pat. No. 5,202,301 discloses removing mercury from liquid hydrocarbon with an activated carbon adsorbent impregnated with a composition containing metal halide or other reducing halide. US Patent Publication No. 2010/0051553 discloses the removal of mercury from liquid streams such as non-aqueous liquid hydrocarbonaceous streams upon contact with a Hg-complexing agent for mercury to form insoluble complexes for subsequent removal. U.S. Pat. No. 8,728,304 describes the removal of trace element levels of heavy metals such as mercury in crude oil by contacting the crude oil with an iodine source, generating a water soluble heavy metal complex for subsequent removal from the crude oil.
Particulate mercury in crudes presents a challenge to the removal of mercury from crude oil as particulate is more difficult to remove than elemental mercury. While some particulate can be removed by filtration, filtration may not be effective in removing particulate mercury when substantial amounts are present in particles below 0.45 μm in diameter. As adsorption technology does not work well for crude oils and condensates with low levels of mercury, and particularly crude oils containing the non-volatile form of mercury, which has not been well addressed in the prior art.
There is a need for improved methods for the removal of mercury from liquid hydrocarbon steams, especially the non-volatile particulate form of mercury. There is also a need for an improved method to manage, control, and remove mercury in produced fluids from a reservoir, e.g., gas, crude, condensate, and produced water.